1. Field
Embodiments of the present disclosure relate to a lighting device and a phosphor plate constituting the lighting device.
2. Background
Low power/high efficiency light sources use a phosphor as low-wave light sources that emit light in a relatively thin spectrum width, and accordingly, in order to be actually used, the phosphor should be converted into white light. During this conversion process, the problem of a reduction in reliability such as deterioration and decomposition of the phosphor caused by a high temperature/high density and low wavelength beam may be generated. In order to solve such a problem, the study regarding the phosphor has been needed so that the light source and the phosphor can be disposed to be separated from each other.
In order to coat the phosphor, a separate base substrate is needed. This substrate simply serves as a support layer of a phosphor film and becomes a factor that causes an increase in material costs for a lighting member. Also, the substrate optically serves as an intermediate layer, thereby causing partial transmittance and light losses. As shown in FIG. 1, when producing a phosphor plate 10, two kinds of phosphors 11, 12 are used in a state of being mixed in order to set a temperature for a specific color. As can be seen from the graph of FIG. 2, absorption wavelengths and emission wavelengths of different kinds of phosphors overlap with each other, thereby causing a reduction of properties.
Also, when the phosphor is applied to lighting as a remote phosphor, a portion of the phosphor exposed to the outside of the lighting has a high possibility of being contaminated by moisture and dust of the outside. Furthermore, a fluorescent screen can be partially damaged due to scratches and the like, and this becomes a main factor of the reduction of optical efficiency. Even though the conventional phosphor may be applied to lighting showing a low output as an UV curing form, it has a limit in extending an application scope because a phosphor layer is easily damaged by heat when the phosphor is applied to lighting showing a high output.
Furthermore, a phosphor plate for an LED element is produced using glass powder (glass frit) and a phosphor. The phosphor plate has a composite structure in which a phosphor based on an inorganic crystal is dispersed in a glass matrix. When producing the phosphor plate by firing glass powder, a structural defect such as pores and the like is generated. Such a structural defect becomes a factor that causes a reduction of strength of the phosphor plate. The structural defect causes destruction or damage by physical damage generated during post processes such as a grinding process, a dicing process, a packaging process or the like and during driving the LED element for a long time.